AHS S130 : Barometric Damper and Flue diameter question

Since the AHS S130 has a 5" flue collar, would a 5" dia. Field Controls RC barometric damper and a 5" flue pipe be my best choice(s) for it, or would it be best to step things up to 6"?

If 5" is adequate, does this seem like a fair deal for a baro damper?

http://www.macwilliamsupply.com/field-c ... -vent.html

I would set it up like axeman recomends, 5" half way threw a 6" T with a 6" barometric damper.

Do you know why they would recommend that configuration? A 5" pipe has roughly 69% of the cross-sectional area of a 6" pipe, but if you extend a 5" pipe half way through a 6" pipe and thereby restrict it by somewhat less than 50% (less than 50% because a 5" pipe inside a 6" will not block the entire width), then in doing so doesn't this in some way restrict the the function of a 6" baro damper enough that a 5" wouldn't perform much differently?

lsayre wrote:Do you know why they would recommend that configuration? A 5" pipe has roughly 69% of the cross-sectional area of a 6" pipe, but if you extend a 5" pipe half way through a 6" pipe and thereby restrict it by nearly 50%, then in doing so doesn't this in some way restrict the the function of a 6" baro damper enough that a 5" wouldn't perform much differently?

It doesn't have any effect on the baro, it just keeps the soot in the pipe instead of your cellar.

I'm assuming that the main pipe is 5" over its entire length, and only the tee and Barometric damper are 6". Am I picturing this correctly in my mind?

There is a reason to make a baro setup exactly as Axeman Anderson directs. You see, the AA exhaust is fan driven and therefore under pressure. If you use a 5" baro or even a 6" baro with a "normal" increaser, then exhaust gasses will tend to come out of the barometric damper. By having the 5" pipe go almost, but not quite, half way into a 6" T, then the gasses are pushed past the baro where the natural draft of the chimney will pick up and exhaust gasses out the chimney. When the fan first starts you might get a small puff out the baro, but within a second all gasses go up the chimney. If you do not do as AA directs, then gasses will constantly come into the boiler room.

Here's a pic looking into a AA baro. You can see how the 5" goes into the 6". It's a home made rig....they all are!

You should use 5" black stove pipe and a 6" Fields RC damper. See my installation photos in this post:

5" up to 6" flu pipe

This concentric pipe install is what A-A recommends in their installation manual. It's especially suitable for high natural draft flues. The baro should go at the chimney thimble. You want the 5" pipe to have the minimum of bends. Eliminate true 90 degree turns and clean out tees. What you are trying to achieve is high stove pipe velocity, ideally laminar flow. When the combustion blower is running this will convey the fly ash to the chimney. There a large change in pressure will occur because the velocity flow goes from 5" to the large chimney area. The fly ash will fall out and drop to the bottom of the chimney. You clean this annually.

There is no need for the more expensive Fields type M in this application. The Type M is for applications requiring more sensitivity in automatic adjustment to flue gas velocity changes. This is not one of those applications, especially with the concentric flue pipe arrangement. You will need a baro to get it set. Depending on your particular chimney you may need to add more weight to the baro flapper. Most certainly ignore the factory engraved settings, they are completely wrong for this use. It's possible you may need to change the position of the two pipes, i.e. how far they fit into each other. They other thing you can do to adjust things is to trim away some of the inter pipe at the damper. This will allow more chimney draft through the damper door rather than going through the 5" pipe. My install has worked well for me.

PS

I found that on very windy days my draft would go higher than it should and I would overheat a little bit. After the first season I added a second baro damper directly across from the one picured. Now if I took that same photo you would see the other damper on the other side. Now on windy days jusssst as the original damper is totally open, the second one opens & the draft stays correct. I keep mine at .02 to .03.

<edit> *smile* We got this one covered times two! LOL

I did mine with all 6", but if I do it again, it will be 5" into 6", with mine I used a small piece of pipe cut down the middle to collapse it, inserted into the T , left it expand and screwed it fast. 5 inch stove pipe is harder to come by. This helps the flyash scoot by the baro (and stay inside) but not 100%

Thanks Freddy and Yanche! The reasoning here is sound, and pictures sure help.

Yanche, what is the pipe sealant that I see in your photos, and what did you use for the 3 x 1/2" spacers?

I've been searching the net, and I'm not finding any single wall 5" stove pipe other than galvanized (which I assume is a big no-no). Do any of you have links that you can provide? Is stainless steel available?

Find a local HVAC supply house. They should have commercial grade pipe in any size and adapters to make it work. You may have to play with the adapter to get the 5" a slip fit.

Freddy wrote:PS

I found that on very windy days my draft would go higher than it should and I would overheat a little bit. After the first season I added a second baro damper directly across from the one picured. Now if I took that same photo you would see the other damper on the other side. Now on windy days jusssst as the original damper is totally open, the second one opens & the draft stays correct. I keep mine at .02 to .03.

<edit> *smile* We got this one covered times two! LOL

Are you using a 6" cross instead of a tee?

5" is out there.

http://www.northlineexpress.com/multipl ... 5BlackPipe